Synthetic resin ion-exchangers are porous polymers having numerous chemical groups with exchangeable ions. In general, they consist of a copolymer framework of styrene and divinylbenzene or styrene and acrylic acid, said framework carrying acid groups, in particular sulfonic acid groups, for cation-exchangers and basic groups (amines) for anion-exchangers. Organic ion-exchangers of the kind having a polymer resin matrix selected from the group consisting mainly of polystyrene resins, polyacrylic resins, polyalkyl amine resins or phenol-formaldehyde resins, which may be present as cation- or anion-exchange resins, depending on their functional groups, and adsorbent resins are described in Ullmann's Encyclopedia of Industrial Chemistry, Fifth Edition, Volume A 14, VCH-Verlagsgesellschaft mbH, Weinheim, Germany 1989 in the chapter "Ion Exchangers", in particular on pages 394-398, and are commercially available under the trade names Lewatit, Dowex, Kastel, Diaion, Relite, Purolite, Amberlite, Duolite, Imac, Ionac, Wofatit. Numerous applications of the ion-exchange resins are also described on pages 399-448 of the cited chapter.
The main purpose of using ion-exchangers is the exchange of undesirable ions present in water for less noxious ions, and the complete removal of ions. If the ions that produce hardness--basically, Ca.sup.2+ and Mg.sup.2+ --are exchanged for Na.sup.+ ions, "hard" water becomes "soft" water. If cations and anions are removed, one obtains demineralized water. Soft water is necessary, for example in the textile industry, and demineralized water in the steam generation, in particular in high-pressure boilers.
In general, ion-exchangers become ineffective by obstruction, i.e. their pores become blocked by suspended particles or inorganic residues, such as iron to compounds. The latter are regularly flushed out, but with time, more pores become progressively blocked and finally the bed has to be replaced. At this point, the problem of disposal of the ion-exchanger arises. As long as no ions that polute the environment are present, the spent ion-exchangers can be disposed of in waste dumps.
Inactive granular organic ion-exchange resins are contaminated with large amounts of inorganic or organic foreign matter, such as suspended particles of all kinds, sludge, microorganisms, algae and various cations, e.g. sodium, potassium, iron, and calcium ions. The amount of these impurities is usually up to 20% by weight, based on the dry substance. The granular ion-exchange resins to be disposed of have in most cases a water content which may amount to up to 50% by weight.